The present invention relates to a component mounting apparatus and method for mounting such components as electronic components, optical components and mechanical components onto a circuit board or other member onto which the components should be mounted. More specifically, the invention relates to an improvement in the positional calibration of the component and the circuit board due to any shift of the optical axis of an image recognition optical system used in the component mounting apparatus or method.
Conventionally, in an electronic component mounting apparatus, an electronic component is mounted onto a circuit board after position recognition of the electronic component and the circuit board is executed by an image recognition optical system for enhanced mounting precision. Then, calibration operation of the image recognition optical system is performed in order to suppress any shift of the mounting position due to distortion of the image recognition optical system or the like caused by changes in environmental temperature around the electronic component mounting apparatus.
Hereinbelow, an example of the electronic component mounting apparatus according to the prior art is described with reference to FIGS. 16 and 17. Referring to FIG. 16, reference numeral 921 denotes an electronic component, which is stored on a tray 922. Reference numeral 923 denotes a head, which sucks up and conveys the electronic component 921. Reference numeral 924 denotes a circuit board, which is sucked up and held to a bonding stage 925. The bonding stage 925 and the tray 922 are fixed on a slide base 926. Reference numeral 927 denotes an image recognition optical system, which performs position recognition of the circuit board 924 and the electronic component 921. Further, the head 923 is movable in an X direction, the slide base 926 is movable in a Y direction and the image recognition optical system 927 is movable in both X and Y directions.
Referring to FIG. 17, reference numeral 928 denotes a CCD camera of the image recognition optical system 927, with a magnifying lens 929 coupled thereto. Reference numeral 930 denotes a prism frame in which a prism 931 is fixed, and the magnifying lens 929 is coupled to this prism frame 930. An image of the electronic component 921 sucked up and held to the head 923 or the circuit board 924 sucked up and held to the bonding stage 925 is taken by the CCD camera 928 via the prism 931 and the magnifying lens 929. Then, the image recognition optical system 927 takes the image of either the electronic component 921 or the circuit board 924 through a switching of the field of view.
With respect to the electronic component mounting apparatus constructed as described above, its operation is described below. First, after the head 923 and the slide base 926 have moved to specified positions, the head 923 moves down to pick up the electronic component 921 on the tray 922. Subsequently, the head 923 and the slide base 926 move again so that a coarse positioning for mounting the electronic component 921 onto the circuit board 924 is performed. Subsequently, for checking the position of the circuit board 924, the image recognition optical system 927 moves to such a position as to bring a feature point on the circuit board 924 into the field of view, performing image recognition of the feature point. Next, for checking the position of the electronic component 921, the image recognition optical system 927 moves to such a position as to bring a feature point on the electronic component 921 into the field of view, performing image recognition of the feature point. Then, position correction between the circuit board 924 and the electronic component 921 is performed based on the image recognition results of the circuit board 924 and the electronic component 921, and on an offset amount (optical-axis shift amount) between a field of view "e" on the electronic-component image recognition side and a field of view "f" on the circuit-board image recognition side which are inputted as previously measured and fixed values. After that, the head 923 moves down to mount the electronic component 921 onto the circuit board 924.
However, with the constitution as described above, even when the image-pickup positions of the electronic component 921 and the circuit board 924 have changed because of distortion of the holding portion of the image recognition optical system 927 due to changes in the room temperature or heat generation inside the apparatus so that the inclination of the optical axis has changed, the position correction would be performed based on a decision that merely the position of the electronic component 921 or the circuit board 924 has changed. As a result, the mounting position of the electronic component 921 is shifted causing change in the inclination of the optical axis.